1. Field of the Invention (Technical Field)
The present invention is generally related to landfill design, construction and operation. More particularly, the present invention is directed to the long-term environmental disposal and treatment of municipal refuse and other types of solid waste by improved processes and landfill design.
2. Background Art
Landfills consist of two basic types. In the "below-ground" mode municipal refuse is placed in a depression in the ground, and in the "above-ground" mode a heap is formed on top of the ground. In each case, refuse is built up within the landfill as a series of approximately ten-foot thick, horizontal layers. As refuse is added to the advancing, inclined face of the top layer, it is compacted with heavy equipment. A daily earthen cover that is approximately one foot thick is placed over the newly-formed area to reduce insect infestation and odor emissions.
In the past, these landfills were not lined at their bottoms. Rain and snowmelt waters would percolate downward through them, biodegradation would occur, and the contaminated leachates that would be formed would seep into the underlying groundwaters. These environmental pollution problems have caused about two-thirds of the landfills in the United States to close down in recent years.
New, much stricter, revisions to the EPA landfill regulations will soon require that landfills have (1) a 30-year post-closure maintenance period, (2) bottom liners and a leachate collection system, and (3) means to detect and prevent the disposal of regulated hazardous wastes and PCB's. These new requirements have caused landfill costs to increase dramatically in recent years.
More modern landfills have their bottoms lined with clay and/or synthetic linings and, after they are completely filled, are capped with layers of clay, synthetic linings, sand, and/or fertile soil. Leakage has been a problem with both these bottom linings and these cap layers. In some cases, differential settling of the landfill has caused the cap layers to rupture. There is a considerable amount of liability associated with these landfills.
The basic problem with these modern landfills is one of leachate control. In the thirty, or more, years that it often takes to build a landfill, rain or snowmelt waters infiltrate its exterior surfaces, react with the refuse, and generate contaminated leachates and methane, carbon dioxide, hydrogen sulfide, and other gases that can pollute both the atmosphere and underground waters. These leachates, which either drain out the bottom of an above-ground landfill or are pumped out of the bottom of a below-ground landfill, must be stored in external reservoirs and/or treated in leachate treatment facilities. In the case of the above-ground landfill, these reservoirs must be large enough to store the landfill's effluent leachates after large rainstorms. The operation of these facilities for up to sixty years constitutes a tremendous operating expense.
One solution that has been used is to minimize rain infiltration by building relatively small (about 24 acres each) and thin (between twenty and thirty feet in thickness) above-ground landfills on a one-at-a-time basis and cover them after they are filled. While this design minimizes leachate generation and gas production, it nevertheless requires relatively large land areas, large amounts of natural building materials (dirt, sand, clay, etc.) and the long-term production of leachates over a large area is still a problem.
Prior to the present invention, no one has developed a landfill design wherein a tall landfill is build with a minimum base area and top cover, a heavy, impermeable cover is built over the entire landfill simultaneously with the construction and filling operations, and the refuse contents are kept in a "dry" state indefinitely. The present invention is designed to accomplish these objectives.
Very heavily built vaults are sometimes used in the prior art to encapsulate hazardous wastes. While they may maintain these wastes in a dry state for very long periods of time, they are much too expensive to be used as repositories for solid wastes that have relatively low levels of contamination.
Over the past twenty years there has been considerable testwork done on a process wherein municipal refuse is contained in a cell with impermeable sides and a dirt-covered top and wetted with recirculated leachates to effect biodegradation to the point where the refuse is environmentally inert. These cells are usually single, lined trenches with a leachate collection zone at their base. They are expensive to build and operate and, because of their depths (twenty to thirty feet), may require excessively long biodegradation periods. Their gas production is poorly contained and recovered, and the long-term environmental security of the process is questionable.
A process and apparatus that is used in the heap leaching of metallic ores has some of the basic design features that are needed to build a tall landfill that could prevent rain infiltration. This process and apparatus, which is described in U.S. Pat. No. 4,526,615, entitled Cellular Heap Leach Process and Apparatus, to Johnson, discloses a heap that is formed by laying layer upon layer of crushed ore on top of impervious interlayers and forming small dirt berms on the tops and bottoms of these ore layers to define individual cells. Leaching solutions are recirculated through these cells to effect leaching of metallic values from crushed ores. This system is not impervious to rain infiltration from the outside, and leachates can move to some degree between cells.
From the foregoing, it will be appreciated that the present invention is a significant advancement in the area of solid waste disposal. The solid waste landfill or repository of the present invention is built and operated so that the contained municipal refuse, or other solid wastes, are maintained in a dry state while the system is being constructed and filled and indefinitely thereafter. In such a system, no leachates are ever generated, and most of the small amount of gases that are formed are separately withdrawn from the system. Also, without biodegradation, differential landfill settling is minimal. Moreover, this landfill has additional significant advancements in that: (1) it has comparatively low capital, operating, and environmental costs; (2) it requires a relatively small area of land on which to build it; (3) it requires relatively small amounts of sand, dirt, clay, etc.; (4) it has aesthetic qualities that make landfills more acceptable to the public; (5) it makes use of several new, more efficient refuse inspection, filling, wet compaction, and daily covering processes; (6) the exterior cover is monitorable on a cell-by-cell basis for leakage and is repairable; (7) when the landfill reaches a tall height it can be used as a hillside site for recreation and sports (e.g., skiing, sledding, climbing, etc.) and, when closed, its top area can be used as view property; (8) it can be advantageously used on many types of solid wastes and some liquid wastes in either small or large facility sizes and in most geographic locations; and (9) it can be used to generate large volumes of valuable methane gas.
These and other objects of the present invention will become more fully apparent in view of the following detailed description, the accompanying drawings, and the appended claims.